Piezoelectric linear step motor

ABSTRACT

A piezoelectric linear stepping motor comprises a cylindrical housing (1), a movable part (4) and fixing devices between them. The fixing devices comprise at least two piezoelectric units (2,3). Each piezoelectric unit (2,3) consists of a shifting (5) and a fixing (6) piezoelectric cells, insulators (7) and a friction element (8). The piezoelectric units (2,3) are disposed inside the housing (1) one behind the other in a longitudinal plane.

TECHNICAL FIELD

The present invention relates to the field of electric motors and, moreparticularly, the invention relates to piezoelectric stepping motors.

BACKGROUND OF THE INVENTION

Known in the art is a linear stepping motor comprising a guide, ahousing and a mover in the form of plates secured in the housing at anangle to the inner surface and frictionally interacting with the guide(SU, A, 801145).

However, this stepping motor has large overall dimensions and mass andperforms the movement with the help of elastic plates, in which case itis impossible to obtain high forces and provide an accurate positioning.

Also known in the art is a piezoelectric linear stepping motorcomprising a housing having fixing units secured in it and a movablepart with a working member (SU, A, 720576).

However, this piezoelectric motor has a great number of components, acomplicated design and is complicative in manufacturing fixing units,and its movable part is liable to an accidental turn in the process oflinear displacement.

SUMMARY OF THE INVENTION

The basic object of the present invention is to create a linearpiezoelectric stepping motor which constructive embodiment would make itpossible to simplify the design and manufacturing technology, to obtainhigh forces at small dimensions and mass of the motor and to increasethe accuracy in positioning the movable part.

This object is achieved by providing a piezoelectric linear steppingmotor comprising a housing having fixing units and a movable part, inwhich motor, according to the invention, the fixing units comprise atleast two piezoelectric units, each piezoelectric unit comprising ashifting piezoelectric cell and a fixing piezoelectric cell separatedfrom each another, from the housing and from the friction element byinsulators, the piezoelectric units are arranged inside the housing onebehind the other in a longitudinal plane or in one transverse plane andhave a form of sectors.

The housing may have a form of a parallelepiped, the piezoelectric unitsmay be made in the form of parallelepipeds and disposed one behind theother in the longitudinal plane, and the movable part may be made in theform of a rod having a rectangular cross section.

The housing may also have a form of a polyhedron, and the piezoelectricunits may be arranged in one transverse plane.

The housing may have cut-out, through which the movable part goesoutside the housing.

The movable part may have at least one guide which enters a respectiveguide on the friction elements.

It is desirable for the motor to have at least two pairs ofpiezoelectric units disposed in the transverse plane.

The piezoelectric cells may be made in the form of a packet ofpiezoelectric plates, rings or their sectors which electrodes areconnected in parallel alternately, in which case the direction ofpolarization of each successive piezoelectric plate, ring, or sector isopposite to that of the previous one.

The gaps between the piezoelectric units are preferably filled with anelastic insulating material.

The housing may be movable and the piezoelectric units may be fixed on astationary rod.

Such constructive embodiment of the piezoelectric linear stepping motorbeing patented makes it possible to simplify the construction andmanufacturing technology, to obtain high forces at a small size and massand to increase the accuracy in positioning the movable part.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference tothe appended drawings, in which:

FIG.1 is a front view of the claimed piezoelectric linear stepping motor(the first embodiment);

FIG.2 is a longitudinal section of the motor shown in FIG.1;

FIG.3 is a front view of the second embodiment of the motor;

FIG.4 is a longitudinal section of the motor shown in FIG.3;

FIG.5 is a front view of the third embodiment of the motor;

FIG.6 is a longitudinal section of the motor shown in FIG.5;

FIG.7 is a front view of the fourth embodiment of the motor;

FIG.8 is a longitudinal section of the motor shown in FIG.5;

FIG.9 is a front view of the fifth embodiment of the motor;

FIG.10 is a longitudinal section of the motor shown in FIG.5;

FIG.11 is a front view of the sixth embodiment of the motor;

FIG.12 is a longitudinal section of the motor shown in FIG.11;

FIG.13 is a front view of the seventh embodiment of the motor;

FIG.14 is a longitudinal section of the motor shown in FIG.13;

FIGS.15-20 are the time steps of the working cycle of the piezoelectriclinear stepping motor.

THE BEST EMBODIMENTS OF THE INVENTION

The piezoelectric linear stepping motor according to the firstembodiment of the invention comprises a cylindrical housing 1 (FIG.1)having inside two piezoelectric units 2 (FIG.2) and 3 and a movable part4 in the form of a cylindrical rod. The piezoelectric units 2 and 3 arerigidly secured to the internal surface of the cylindrical housing 1.

Each piezoelectric unit 2 and 3, respectively, consists of a shiftingpiezoelectric cell 5, a fixing piezoelectric cell 6, insulators 7 and afriction element 8 jointed together.

Each shifting piezoelectric cell 5 has a vector of its initialpolarization directed at an angle to the longitudinal axis of the motor.And the fixing piezoelectric cells 6 have a vector of their initialpolarization directed perpendicularly to the longitudinal axis of themotor.

The insulators 7 provide insulation of the shifting 5 and fixing 6piezoelectric cells from each other and from the housing 1 and thefriction element 8. The friction element 8 is split to provide tightersqueezing of the movable part 4 by the piezoelectric units 2 and 3.

Each piezoelectric cell has electrodes connected to wires (not shown inthe drawing).

The gaps between the piezoelectric units 2 and 3 are filled with anelastic insulating material 9.

On the surface of the movable part 4 a guide 10 (FIG. 1) is made whichenters the corresponding guide on the friction elements 8. The guide 10excludes a possibility of the radial displacement of the cylindricalrod.

Other embodiments of the piezoelectric linear stepping motor, accordingto the invention, are possible. In these embodiments, character 2'-9',2"-9", and 2'"-9'", respectively, represent parts analogous to thoserepresented by characters 2-9, respectively, of the first embodiment.

In the second embodiment of the motor, in contrast with the firstembodiment, piezoelectric units 2' (FIGS.3 and 4) and 3' are disposed inone transverse plane and made in the form of sectors. This considerablyreduces the overall dimensions and mass of the motor.

The third embodiment of the motor, having characters 2"-9" differs fromthe first one by the form of the housing and the movable part, as wellas by a construction of the piezoelectric units and cells that issimpler in manufacture. The housing 11 (FIGS.5 and 6) has a form of aparallelepiped and the movable part is made in the form of a rod 12 of arectangular cross section.

In the fourth embodiment of the motor the housing 13 is made in the formof a polyhedron and piezoelectric units 2'" and 3'" are disposed in onetransverse plane.

In the fifth embodiment of the motor the housing 14 (FIGS.5 and 10) hasa cut-out 15, through which the movable part 16 goes out of the housing14. The design of piezoelectric units 2" and 3" is similar to that ofthe third embodiment.

In the sixth embodiment the movable element is the housing 17 (FIGS. 11and 12) and the stationary element is a bar 18, to which thepiezoelectric units 2 and 3 are rigidly secured.

In the seventh embodiment, like in the sixth one, the housing 17 (FIGS.13 and 14) is a movable element and the rod 18 is a stationary element,the piezoelectric units 2" and 3" being rigidly secured to the rod 18and are made in the form of sectors disposed in one transverse plane.

The motor according to the invention operates as follows, using thefirst embodiment by example.

The piezoelectric units 2 (FIG. 2) and 3 are made from identicalshifting piezoelectric cells 5 and fixing piezoelectric cells 6. Theoperation of the piezoelectric units 2 and 3 is executed when a voltageof a respective polarity is applied on the electrodes of thepiezoelectric cells. When the positive voltage is applied to theelectrodes of the shifting piezoelectric cells 5, the inversepiezoelectric effect results in a displacement of the internal partleftwards relative to the external part secured in the housing 1. Whenthe positive voltage is applied to the fixing piezoelectric cells 6,they clamp the movable part 4, because the vector of their polarizationis directed perpendicularly to the longitudinal axis of the motor. Theapplication of the negative voltage results in a reverse action: theshifting piezoelectric cells 5 move rightwards, while the fixingpiezoelectric cells 6 are pushed apart from the movable part 4.

The working cycle consists of six time steps.

The position corresponding to the first time step is shown in FIG.15.The positive voltage is applied to the shifting piezoelectric cell 5 ofthe piezoelectric unit 2 and to the fixing piezoelectric cells 6 of thepiezoelectric units 2 and 3, and the negative voltage is applied to theshifting piezoelectric cell 5 of the piezoelectric unit 3. In this casethe shifting piezoelectric cell 5 of the piezoelectric unit 3 isdisplaced rightwards while the shifting piezoelectric unit 5 of thepiezoelectric unit 2 is displaced leftwards, the fixing piezoelectriccells 6 of both piezoelectric units squeeze the movable part 4 throughthe friction elements 8.

In the second time step the negative voltage is applied to the fixingpiezoelectric cell 6 of the piezoelectric unit 6 (FIG. 16), and it ispushed apart from the movable part 4.

In the third time step the negative voltage is applied to the shiftingpiezoelectric cell 5 (FIG. 17) of the piezoelectric unit 2 and thiscell, moving rightwards, displaces the fixing piezoelectric cell 6 andthe movable parts 4 rightwards for one step. At the same time, thepositive voltage is applied to the shifting piezoelectric cell 5 of thepiezoelectric unit 3 and the latter moves leftwards together with thefixing piezoelectric cell 6.

In the fourth time step the positive voltage is applied to the fixingpiezoelectric cell 6 (FIG. 18) of the piezoelectric unit 3 and itsqueezes the movable part 4.

In the fifth time step the negative voltage is applied to the fixingpiezoelectric cell 6 (FIG. 19) of the piezoelectric unit 2 and it ispushed apart from the movable part 4.

In the sixth time step the piezoelectric units 2 (FIG. 20) and 3 goapart i.e. the positive voltage is applied to the electrodes of theshifting piezoelectric cell 5 of the piezoelectric unit 2, and the unit2 moves leftwards, whereas the negative voltage is applied to theshifting piezoelectric cell 5 of the piezoelectric unit 3 and it movesrightwards together with the fixing piezoelectric cell 6 and movablepart 4. The movable part 4 is displaced for one more step. In so doingthe working cycle is completed, the movable part 4 is displaced for twosteps.

Then the process of linear displacement is continued in the samesequence.

In the process of the displacement of the housing the same working cycleis used but the shifting piezoelectric cells and fixing piezoelectriccells change places.

The reversing is executed by changing the sequence in applying thevoltage to the fixing piezoelectric cells.

The use of several piezoelectric units connected in series will make itpossible to increase considerably the force on the movable part.

The claimed piezoelectric stepping motor has a simple design andmanufacturing technology, a small size and mass, a high force on themovable part and makes it possible to increase the positioning accuracyand to provide a uniform linear displacement.

In the description of the embodiments of the invention, for betterunderstanding, a specific narrow terminology is used. However, theinvention is not limited by the accepted terms and one should keep inmind that each such term covers all equivalent terms for the unitsworking in a similar manner and used for the solution of the sametechnical problems.

Although the present invention is described in connection withpreferable type of its realizations, it is clear that changes andmodifications may be made without deviation from the idea and scope ofthe invention and those skilled in the art may easily understand that.

These changes and modifications are considered not extending beyond theessences and scope of the invention and the appended claims.

Industrial Applicability

The invention can be used as a slave mechanism in electricalengineering, radio engineering and automation technology.

What is claimed is:
 1. A piezoelectric linear stepping motor comprisinga housing having fixing units secured therein and a part movablerelative to the housing, wherein the fixing units comprise at least twopiezoelectric units, each piezoelectric unit comprising a shiftingpiezoelectric cell and a fixing piezoelectric cell separated from eachother, from the housing and from a friction element by insulators, thefixing piezoelectric cells having a vector of polarization perpendicularto a longitudinal axis of the motor, and the shifting piezoelectriccells having a vector of polarization at an acute angle to thelongitudinal axis of the motor, the piezoelectric units are disposedinside the housing one behind the other in a longitudinal plane, wherebythe fixing cells sequentially engage and disengage the movable part, togrip the movable part, and whereby the shifting cells linearly shift themovable part.
 2. The piezoelectric linear stepping motor as claimed inclaim 1, wherein the housing has a form of a parallelepiped, thepiezoelectric units are made the form of parallelepipeds disposed onebehind the other in the longitudinal plane, and the movable part is madein the form of a rod having a rectangular cross section.
 3. Thepiezoelectric linear stepping motor as claimed in claim 1, wherein thehousing has a cut-out through which the movable part goes out of thehousing.
 4. The piezoelectric linear stepping motor as claimed in claim1, wherein the movable part has at least one guide which enters acorresponding guide on the friction elements.
 5. The piezoelectriclinear stepping motor as claimed in claim 1, wherein the piezoelectricunits are made in the form of a packet of piezoelectric plates, rings ortheir sectors which electrodes are connected in parallel alternately, inwhich case the direction of polarization of each successivepiezoelectric plate, ring, or sector is opposite to that of the previousone.
 6. The piezoelectric linear stepping motor as claimed in claim 1,wherein the gaps between the piezoelectric units are filled with anelastic insulating material.
 7. The piezoelectric linear stepping motoras claimed in claim 1, wherein the housing is movable and thepiezoelectric units are secured on a stationary rod.
 8. A piezoelectriclinear stepping motor according to claim 1, wherein the shifting cellsand fixing cells of the first and second piezoelectric units arecylindrical.
 9. A piezoelectric linear stepping motor comprising ahousing having fixing units secured therein and a part movable relativeto the housing, wherein the fixing units comprise at least twopiezoelectric units, each piezoelectric unit comprising a shiftingpiezoelectric cell and a fixing piezoelectric cell separated from eachother, from housing and from a friction element by insulators, thefixing piezoelectric cells having a vector of polarization perpendicularto a longitudinal axis of the motor, and the shifting piezoelectriccells having a vector of polarization at an acute angle to thelongitudinal axis of the motor, the piezoelectric units are disposedinside the housing in the same transverse plane and have a form ofsectors, whereby the fixing cells sequentially engage and disengage themovable part, to grip the movable part, and whereby the shifting cellslinearly shift the movable part.
 10. The piezoelectric linear steppingmotor as claimed in claim 9, wherein the housing has a form of apolyhedron and the piezoelectric units are disposed in one transverseplane.
 11. The piezoelectric linear stepping motor as claimed in claim9, wherein it has at least two pairs of piezoelectric units disposed ina transverse plane.
 12. A piezoelectric linear stepping motor accordingto claim 9, wherein the housing has a cut-out through which the movablepart goes out of the housing.
 13. A piezoelectric stepper motoraccording to claim 9, wherein the movable part has at least one guidewhich enters a corresponding guide on the friction elements.
 14. Apiezoelectric linear stepping motor according to claim 9, wherein thepiezoelectric units are made in the form of a packet of piezoelectricplates, rings or their sectors which electrodes are connected inparallel alternately, in which the the direction of polarization of eachsuccessive piezoelectric plate, ring or sector is opposite to that ofthe previous one.
 15. A piezoelectric linear stepping motor according toclaim 9, wherein the gaps between the piezoelectric units are filledwith an elastic insulating material.
 16. A piezoelectric linear steppingmotor according to claim 9, wherein the housing is made movable, and thepiezoelectric units are secured on a stationary rod.
 17. In apiezoelectric linear stepping motor having a longitudinal axis andhaving piezoelectric cells and a movable shaft, a method of moving theshaft in a single axial direction, comprising the steps of:a)frictionally engaging the shaft with first and second fixingpiezoelectric cells, the first fixing piezoelectric cell being in afirst axial position, the second piezoelectric cell being in a secondaxial position; b) releasing the shaft with the second fixingpiezoelectric cell so that only the first fixing piezoelectric cellremains frictionally engaged to the shaft; c) shifting the first andsecond fixing piezoelectric cells in opposite axial directions so thatthe first fixing piezoelectric cell is shifted to a third axial positionand the second fixing piezoelectric cell is shifted to a fourth axialposition, thereby moving the shaft in the single axial direction; d)frictionally engaging the shaft with the second fixing piezoelectriccell; e) releasing the shaft with the first fixing piezoelectric cell sothat only the second fixing piezoelectric cell remains frictionallyengaged to the shaft; f) shifting the first and second fixingpiezoelectric cells so that the first fixing piezoelectric cell isaxially shifted back to the first axial position and the secondpiezoelectric cell is axially shifted back to the second axial position,thereby moving the shaft in the single axial direction; and g) repeatingsteps a) through f) to move the shaft, whereby the shaft is moved twosteps in the single axial direction each time steps a) through f) areperformed.
 18. The method of claim 17, wherein steps c) and f) areperformed by applying voltage to shifting piezoelectric cells coupled tothe fixing piezoelectric cells.
 19. In a piezoelectric linear steppingmotor having a longitudinal axis and having piezoelectric cells and amovable housing, a method of moving the housing in a single axialdirection, comprising the steps of:a) frictionally engaging the housingwith first and second fixing piezoelectric cells, the first fixingpiezoelectric cell being in a first axial position, the secondpiezoelectric cell being in a second axial position; b) releasing thehousing with the second fixing piezoelectric cell so that only the firstfixing piezoelectric cell remains frictionally engaged to the housing;c) shifting the first and second fixing piezoelectric cells in oppositeaxial directions so that the first fixing piezoelectric cell is shiftedto a third axial position and the second fixing piezoelectric cell isshifted to a fourth axial position, thereby moving the housing in thesingle axial direction; d) frictionally engaging the housing with thesecond fixing piezoelectric cell; e) releasing the housing with thefirst fixing piezoelectric cell so that only the second fixingpiezoelectric cell remains frictionally engaged to the housing; f)shifting the first and second fixing piezoelectric cells so that thefirst fixing piezoelectric cell is axially shifted back to the firstaxial position and the second piezoelectric cell is axially shifted backto the second axial position, thereby moving the housing in the singleaxial direction; and g) repeating steps a) through f) to move thehousing, whereby the housing is moved two steps in the single axialdirection each time steps a) through f) are performed.
 20. In apiezoelectric linear stepping motor having a longitudinal axis andhaving piezoelectric cells and a movable part, a method of moving themovable part in a single axial direction, comprising the steps of:a)frictionally engaging the movable part with first and second sets offixing piezoelectric cells, the first set of fixing piezoelectric cellsbeing in a first set of axial positions, the second set of piezoelectriccells being in a second set of axial positions; b) releasing the movablepart with the second et of fixing piezoelectric cells so that only thefirst set of fixing piezoelectric cells remains frictionally engaged tothe movable part; c) shifting the first and second sets of fixingpiezoelectric cells in opposite axial directions so that the first setof fixing piezoelectric cells is shifted to a third set of axialpositions and the second set of fixing piezoelectric cells is shifted toa fourth set of axial positions, thereby moving the movable part in thesingle axial direction; d) frictionally engaging the movable part withthe second set of fixing piezoelectric cells; e) releasing the movablepart with the first set of fixing piezoelectric cells so that only thesecond set of fixing piezoelectric cells remains frictionally engaged tothe movable part; f) shifting the first and second fixing piezoelectriccells so that the first set of fixing piezoelectric cells is axiallyshifted back to the first set of axial positions and the second set ofpiezoelectric cells is axially shifted back to the second et of axialpositions, thereby moving the movable part in the single axialdirection; and g) repeating steps a) through f) to move the movable partin the single axial direction.
 21. The method of claim 20, wherein stepsc) and f) are performed by applying voltage to sets of piezoelectricshifting cells coupled to the sets of fixing piezoelectric cells.